Numerous natural gas wells produce what is called “sour gas”, i.e. natural gas comprising acidic compounds such as carbon dioxide and/or sulphur compounds such as H2S, sulphides, disulphides and thiophenes. The total amount of acidic compounds is generally too high, making the natural gas unsuitable for direct use. Depending on the intended use of the natural gas, acidic compounds often have to be removed.
Concentrations of carbon dioxide of lower than 50 ppmv are often desired. In addition, sales gas specifications often mention total concentrations of sulphur compounds lower than 10 ppmv, or even as low as less than 4 ppmv.
Processes for the removal of carbon dioxide from natural gas are known in the art and are generally based on physical and/or chemical absorption.
Physical absorption processes suffer from the fact that removal of hydrogen sulphide and/or carbon dioxide is often accompanied with undesired removal of valuable hydrocarbons.
Chemical absorption processes in general are able to remove carbon dioxide and/or hydrogen sulphide without much difficulty. However, they suffer from the fact that large amounts of waste are produced.
In the event that the natural gas comprises other contaminants, especially sulphur contaminants such as hydrogen sulphide, solid bed adsorption process are often used in combination with liquid absorption processes to remove these sulphur contaminants. Solid bed adsorption processes generally are suitable for adsorption of relatively small amounts, typically below 0.5% of acidic compounds. Adsorption of larger amounts of acidic compounds requires the use of very large adsorbent beds. Large solid adsorbent beds take relatively more time for regeneration and disproportionately high quantities of regeneration gas are needed.
Therefore, there remains a need in the art for a simple and efficient process to remove carbon dioxide from natural gas, thereby obtaining a purified gas stream.